Associating a requester with multiple sites

Some accounts have people who work across all sites in that account. They might be in a call center or the IT department that handles all sites for that account. They use one email address.

Currently, a requester once created has a site that is associated with their account. Once a ticket comes in from an associated requester there is no way to change the site or even the requester. It would be useful if we could add multiple sites to the requester so that if it was assigned to the wrong site we could chose the appropriate site from the drop down.